1. Field of the Invention
The present invention relates to an image display device that has substrates opposed to each other and a plurality of electron sources arranged on the inner surface of one of the substrates. The invention also relates to a method of manufacturing a spacer for use in the image display device and to an image display device that has spacers manufactured by the method.
2. Description of the Related Art
In recent years, there have been demands for image display devices for high-grade broadcasting or high-resolution versions therefor, which require stricter screen display performance. To meet these demands, the screen surface must be flattened and enhanced in resolution. Moreover, the devices must be lighter and thinner.
Flat image display devices, such as a field emission display (hereinafter referred to as FED), are promising as image display devices that fulfill the above requirements. The FED has a first substrate and a second substrate that are opposed to each other, with a given gap between them. The substrates have their respective peripheral edge portions joined directly or by a sidewall shaped like a rectangular frame. Thus, the substrates constitute a vacuum envelope. Phosphor layers are formed on the inner surface of the first substrate. A plurality of electron-emitting elements, which are used as electron sources that excite the phosphor layers, causing them to emit light, are provided on the inner surface of the second substrate.
A plurality of spacers, or support members, are arranged between the first and second substrates in order to support the atmospheric load that acts on these substrates. In displaying an image on the FED, anode voltage is applied to the phosphor screen, and electron beams emitted from the electron emitting elements are accelerated by the anode voltage as they hit the phosphor screen, thereby causing the phosphors to glow and display a video image.
In an FED of this type, each electron-emitting element has a size on the micrometer order, and the distance between the first substrate and the second substrate can be on the millimeter order. Thus, this image display device can achieve higher resolution and can be lighter and thinner than cathode-ray tubes (CRTs) that are used as displays of existing television receivers or computers.
The image display device of the type described above must have practical display characteristics. To this end, the anode voltage should preferably be several kilovolts or more with use of phosphors that are similar to those of a conventional cathode-ray tube. In view of the resolution and the properties and manufacturability of the support members, however, the gap between the first and second substrates cannot be large. It must be about 1 mm to about 3 mm. Inevitably, secondary electrons and reflected electrons are generated when electrons emitted from the second substrate impinge on the spacers. Consequently, the spacers are electrically charged. Generally, the spacers are charged positively at the acceleration voltage of the FED. As a result, the spacers attract the electron beams emitted from the electron-emitting elements, deflecting the electron beams from their original paths. This results in erroneous landing of the beams on the phosphor layers and ultimately lowers the color purity of the image displayed.
To reduce the attraction of electron beams to the spacers, each spacer may be rendered electrically conductive at its entire surface or at a part thereof. U.S. Pat. No. 5,726,529, for example, discloses a structure in which an insulating spacer is rendered electrically conductive at one end close to the second substrate. Thus, the spacer is prevented from being electrically charged.
If the spacers are rendered electrically conductive, however, an ineffective current flowing from the first substrate to the second substrate will increase. This raises the temperature and increases the power consumption. Further, the conventional process of rendering the spacers electrically conductive cannot help but increase the manufacturing cost.